1. Field of the Invention
The present invention relates generally to VTOL aircraft, and more particularly to an improved VTOL aircraft and ducted fan propulsion system wherein the ducts housing the engines remain stationary with their axial center lines approximately parallel with the center line of the fuselage, and the thrust is selectively vectored by adjustable vanes mounted in the aft portion of each duct.
2. Brief Description of the Prior Art
Over the past 53 years, inventors have attempted to create a vehicle that could be flown in the air as well as driven on land. According to an article in the February 1989 issue of Smithsonian Magazine, more than 30 designs for flying cars have been submitted to the U.S. Patent Office since 1936. These early designs combined elements of the automobile with those of the airplane. Since the fuselage of the craft was large, usually the size of a passenger compartment of a car, a huge, powerful engine and large wings were needed to generate enough thrust and lift to make the craft airborne. On the ground, the huge engine was unnecessary and thus inefficient, the exposed propeller (if one was used) was a safety hazard, and the large wings had to be removed and stored prior to driving the craft on the road.
The present invention is an aircraft that can be used as a land vehicle efficiently and without modification. A major difference between the present invention and the prior car/plane inventions is that the present invention is all one structure so it provides efficiency in the air as well as on the ground. Ducted fans are used instead of exposed propellers so safety is not compromised. Half of the engines can be shut down for fuel conservation and efficient operation of the aircraft while being driven on land. Additionally, the outboard segments of the short wings are hinged to be folded easily, and thus do not have to be removed from the craft prior to driving.
Another feature of the present invention is that it is capable of vertical takeoff and landing (VTOL) by vectoring the fan thrust from the ducted fan engines. Previous VTOL efforts have relied on fixed orientation of the duct centerlines vertically for hover and then re-directing their thrust with vanes for transition into forward flight. This method was used with rigid re-directing vanes that would stall the airflow at angles above 15 degrees. This rigid vane approach resulted in a limited ability to generate a significant transverse force for acceleration. The alternative has been VTOL aircraft that have tilted the entire duct or the exposed propeller, whichever was used, in order to vector the thrust. A tiltable duct or propeller requires complex structural, electrical and mechanical connections. Furthermore, the tilting duct or propeller experiences off-axis flow into the inlet during transition into forward flight, resulting in flow separation at the upstream inlet lip. The rotation of the duct or propeller is inherently slow to react and cannot be modulated to provide the fast response time that is required for longitudinal control. Additionally, the tilting duct is not an efficient annular airfoil, and therefore additional wing area must be provided for aerodynamic lift. This greater wing area results in additional drag.
U.S. Pat. No. 4,358,074 shows a propulsion system for VTOL aircraft having stationary ducts which vector the airflow by utilizing a movable, fixed camber, cascading vane system in addition to a slotted flap system. The airflow within the nacelle is divided into twin airstreams. One of the airstreams is directed downwardly through the fixed camber vane system. The other airstream is exhausted through an aft nozzle at the outlet, against a slotted flap system mounted on a wing located immediately behind the duct. The fixed camber vane system can only direct a limited amount of airflow through very modest angles before the flow separates creating large pressure and thrust losses. The divided airstream system is required because it would be difficult to deflect the full airstream through large angles by utilizing the wing flap system alone.
Variable camber flow deflector blades, in which each blade (similar to a vane) is capable of resiliently deforming to affect airflow direction, are the subject of U.S. Pat. No. 4,235,397. In this patented invention, the leading edge of the blade is anchored and the trailing edge of the blade is affixed to a mechanism which pulls the trailing edge downward in an arc, so that the blade is effectively bent, thereby re-directing the airflow. This configuration requires that the blade be great enough in width to house an effective leaf spring member and it also limits the materials that the blade skin and filler can be made of. Another type of airfoil variable cambering device is the subject of U.S. Pat. No. 4,247,066. Both of these patented inventions utilize mechanical parts that are subject to high stress loads. These complex mechanical devices are slow to react due to the particular interaction of the mechanical parts and cannot provide the fast response times desirable for attitude and altitude control.